1. Field of the Invention
The present invention relates to a keyswitch device and to a keyboard which is provided with the keyswitch device.
2. Description of the Related Art
A keyswitch device is used in control panels, etc., of industrial machinery for inputting predetermined information to a main apparatus. Alternatively, a keyboard which is provided with a plurality of keyswitch devices is used. In a keyboard, keyswitch devices are arranged for specific predetermined information. On the surfaces of each keytop, a letter to be input or control content or other input information is engraved. When a keytop is pushed, a key input signal which corresponds to the input information which is engraved on the keytop is sent to the main apparatus. Such a keyboard is used not only for control panels of industrial machinery, but also POS (Point of Sales) systems of stores etc.
Japanese Patent Publication No. 2003-263931A discloses an operating device comprising a board on the surface of which a pair of conductor patterns are formed and with the pair of conductor patterns connected to each other. In this operating device, a pushing member is arranged facing the pair of conductor patterns. The pushing member is supported by an elastic member to be able to move in the up-down direction. The elastic member is provided with a contact which faces the conductor patterns. It is disclosed that electrical connection of the pair of conductor patterns is obtained by the contact touching the pair of conductor patterns.
Japanese Patent Publication No. 2-132718A discloses a membrane switch which comprises a lower electrode pattern which is formed integrally with the main apparatus and an upper electrode which is arranged at a back surface of a pushing part of the keyboard and faces the lower electrode pattern. In this membrane switch, it is disclosed that an adhesive tape or a binder and the work of applying these are not required, since the lower electrode is formed integrally with the main apparatus.
In a keyswitch device which is used for industrial machinery etc., by providing a disc spring and pushing the keytop, the disc spring is inverted to obtain electrical connection. Such a device is being often employed.
Further, a keyswitch device of the membrane contact type is also being employed. A membrane contact type keyswitch device is provided with membrane sheet. The membrane sheet is pushed to obtain electrical connection. The membrane sheet may be directly pushed or may be pushed by a hollow elastic member called a “rubber cup”. A keytop is, for example, arranged at the top surface of a semispherical rubber cup and is supported by the rubber cup. In this case, a mechanism with no member for guiding sliding of the keytop is often employed.
In particular, in industrial machinery etc., sometimes oil, dust, or other foreign matter enters the keyswitch device. When a member is arranged for guiding the keytop by sliding, if foreign matter enters the keyswitch device, the keytop will no longer be able to smoothly move. For this reason, a mechanism which comprises only the above such rubber cup to support the keytop is mainly used.
In this regard, in recent years, sometimes it is desired to push a single keytop so as to connect two independent electrical circuits. In such a device, by arranging two contact pairs for one electrical circuit and another electrical circuit inside a single keyswitch device and pushing the keytop, it is possible to simultaneously connect the two contact pairs.
In such a keyswitch device which simultaneously connects two contact pairs, there was the problem that the above such mechanism which is provided with a disc spring or mechanism which uses a rubber cup to support the keytop was not suitable. For example, in a mechanism which uses a rubber cup to support the keytop, if pushing a position which deviates from the center of the keytop, the keytop would end up tilting, so sometimes the two contact pairs cannot be stably connected.